1. FIELD OF THE INVENTION
This invention relates to an improved method of forming epitaxial Si-Ge heterostructures.
2. DESCRIPTION OF THE BACKGROUND ART
Epitaxial Ge-Si heterostructures are currently of interest due to their potentially useful optical- and electronic properties. At this point, high quality strained Si-Ge/Si layers have been produced by molecular beam epitaxy (MBE) (J. C. Bean, L. C. Feldman, A. T. Fiory, S. Nakahara, and I. K. Robinson. J. Vac. Sci. Technol. A 2, 436 (1984)) and chemical vapor deposition (CVD) (C. M. Gronet, C. A. King, W. Opyd, J. F. Gibbons, S. D. Wilson, and R. Hull. J. Appl. Phys. 61, 2407 (1987)). A technique such as MBE allows precise control on the scale of a fraction of a monolayer, thus allowing possible band structure engineering and tailoring of the transport and optical properties of this system (J. Bevk, J. P. Mannaerts, L. C. Feldman, B. A. Davidsov, and A. Ourmazd. Appl. Phys. Lett. 49, 286 (1986)).
There are several inherent problems with these techniques, however. First of all, they require extremely low interfacial contamination and precise temperature control. If there is any contamination at the Si-Ge/Si interface and. if the temperature is not precise, Si-Ge heterostructures will not form. Consequently, the set-ups for these processes are quite expensive. In addition, wafer size limitations exist because only certain size wafers will fit into the MBE machine.
Investigations of the formation of epitaxial Ge-Ge and Si-Si heterostructures by solid phase epitaxial (SPE) regrowth of evaporated amorphous films (M. G. Grimaldi, M. Maenpaa, B. M. Paine, M-A. Nicolet, S. S. Lau, and W. F. Tseng. J. Appl. Physics. 52, 1351 (1981)) have also been made. Again, there is the problem of contamination. Interfacial contamination is a very important consideration since results indicate that a very clean interface between the Si substrate and the amorphous layer must exist before any SPE can occur. Recently, SPE of amorphous Ge layers has been achieved by Abelson et al., produced by pulsed laser mixing (J. R. Abelson, T. W. Sigmon, Ki Bum Kim, and K. H. Weiner, Appl. Phys. Lett. 52, 230 (1988)). In this case, the Si and amorphous Ge interface is melted during the laser annealing, allowing SPE to occur. However, SPE, in the above methods, does require vacuum deposition.
Finally, Fathy et al. have reported on the formation of an epitaxial SiGe layer following the wet oxidation of a germanium-implanted silicon substrate (D. Fathy, 0. W. Holland, and C. W. White, Appl. Phys. Lett. 51, 1337 (1987)). Unfortunately, implantation processes are very expensive and require extensive and expensive equipment.